The availability of a satellite based Global Positioning System (GPS) has revolutionized geo-positioning and created new applications and/or commercially practical devices that incorporate geo-positioning into their operations. Examples of uses for automated geo-positioning that have been recently created or greatly expanded include moving map displays for use in automobiles and tracking of cargo shipments moving by truck, rail or other modes. Recent interest in using geo-positioning capabilities in cellular phones arose as a means to include geo-position with cellular phone calls, such as for the Enhanced 911, or E911, service mandated by the Federal Communications Commission (FCC) for locating cellular phones during a 911 call.
Wireless radio receivers, such as GPS receivers, are increasingly being included in portable, battery powered devices. Such portable devices, which include cellular phones, place energy consumption at a premium and strive to minimize energy consumption. Modern cellular phone communications protocols allow cellular receivers to operate with low power consumption by the portable cellular phones using those protocols. The GPS signal protocol, however, does not include features that facilitate lowering energy consumption in a receiver.
GPS radio signals are relatively low power signals transmitted at high RF frequencies. These characteristics result in great difficulty in receiving these signals in some areas, such as indoors or in sheltered areas. Portable GPS receivers are operated continuously or with a constant periodicity at times when no GPS signal is able to be received by the receiver so that the GPS signal can again be received and processed when the GPS receiver is relocated to a location where the GPS signal can be received. This causes the receivers to consume energy even when the probability of successful operation is low. This wastes energy, which is at a premium in portable devices.
Thus, there is a need for solving the problems with the prior art as described above, and in particular for an improved method for operating wireless receivers, such as GPS receivers, so as to improve power consumption and improve successful reception performance.